Effect of Parathyroid Hormone on the Connecting Tubule from the Rabbit Kidney: Biphasic Response of Transmural Voltage

The effect of parathyroid hormone (PTH) on ion transport was examined by observing transmural (VT) and basolateral membrane voltage (VB) in the in vitro perfused rabbit connecting tubule. Addition of 10 nmol/l PTH to the bath induced a biphasic response of VT, with hyperpolarization followed by depolarization. Chlorophenylthioadenosine cyclic 3',5'-monophosphate mimicked the effect of PTH, which did not change the VB in the connecting tubule cell, but mainly caused changes in the apical membrane voltage. The VT of distal convoluted tubule and the cortical collecting duct were not affected by PTH. Elimination of Na+ from the lumen abolished the PTH-induced VT responses in the connecting tubule. In the presence of 10 mumol/l amiloride, PTH caused an initial hyperpolarization but did not induce the late depolarization. The same was seen in the absence of luminal Ca2+. Either addition of 0.1 mmol/l ouabain to the bath or elimination of bath Na+ completely abolished the PTH-induced VT changes. The presence of 5 mmol/l Ba2+ in the lumen did not affect the response to PTH. These findings indicate that the initial hyperpolarization may be caused by an increase in Na+ influx across the luminal membrane through an amiloride-insensitive Na+ conductive pathway and that the late depolarization may be caused by the decrease in Na+ influx through the amiloride-sensitive Na+ conductive pathway. Luminal Ca2+ is necessary for the late depolarization caused by PTH.(ABSTRACT TRUNCATED AT 250 WORDS)